Technique to diagnose and control ammonia generation from a twc for passive ammonia scr operation

Method for controlling ammonia generation in an exhaust gas feedstream output from an internal combustion engine equipped with an exhaust aftertreatment system including a three-way catalytic device and an ammonia-selective catalytic reduction device, comprising:

• executing an ammonia generation cycle to generate ammonia on the three-way catalytic device, said ammonia generation cycle comprising;
• operating the engine at a rich of stoichiometry air-fuel ratio to generate an engine-out exhaust gas feedstream including nitric oxide, carbon monoxide, hydrogen and unburned hydrocarbons that converts to ammonia on the three-way catalytic device;
• monitoring an air-fuel ratio in the exhaust gas feedstream upstream of the three-way catalytic device;
• monitoring an air-fuel ratio in the exhaust gas feedstream downstream of the three-way catalytic device;
• comparing the air-fuel ratio upstream of the three-way catalytic device and the air-fuel ratio downstream of the three-way catalytic device;
• and
• if the air-fuel ratio downstream of the three-way catalytic device is less than the air-fuel ratio upstream of the three-way catalytic device, adjusting operation of the engine to generate a leaner air-fuel ratio of engine-out exhaust gas feedstream until the air-fuel ratio downstream of the three-way catalytic device is equal to the air-fuel ratio upstream of the three-way catalytic device.

An exhaust aftertreatment system for an internal combustion engine, comprising:

• a catalytic device formulated to produce ammonia from an exhaust gas feedstream that includes nitric oxide, carbon monoxide, hydrogen and unburned hydrocarbons, the catalytic device close-coupled to an exhaust manifold of the internal combustion engine and fluidly coupled to an ammonia-selective catalytic reduction device located downstream of the catalytic device;
• a first wide-range air-fuel ratio sensor located upstream of the catalytic device and a second wide-range air-fuel ratio sensor located downstream of the catalytic device, the first and second wide-range air-fuel ratio sensors each configured to generate a linear signal corresponding to air-fuel ratio over an air-fuel ratio range;
• a control module configured to
• initiate an ammonia generation cycle to generate ammonia on the catalytic device;
• monitor an air-fuel ratio in the exhaust gas feedstream upstream of the catalytic device;
• monitor an air-fuel ratio in the exhaust gas feedstream downstream of the catalytic device;
• compare the air-fuel ratio upstream of the catalytic device to the air-fuel ratio downstream of the catalytic device;
• and
• if the air-fuel ratio downstream of the catalytic device is richer than the air-fuel ratio upstream of the catalytic device, adjust operation of the engine until the air-fuel ratio downstream of the catalytic device is equal to the air-fuel ratio upstream of the catalytic device.